The Straits Times Index (SGX: ^STI) has had a terrific run.
The SPDR STI ETF (SGX: ES3), which tracks the STI, returned 13.1% in the first half of 2026 (1H2026).
And the banks have done most of the heavy lifting.
In the first half of 2026 alone, OCBC Limited (SGX: O39) returned 28%, while DBS Group Holdings (SGX: D05) and UOB Limited (SGX: U11) returned at 19% and 15%, respectively.
This raises an uncomfortable question.
If DBS, OCBC and UOB were to sell off hard, what would happen to the STI?
Would the index simply go down with them, or could the rest of the index cushion the blow?
Why Singapore Banks Matter So Much to the STI
The STI is market-capitalisation-weighted: bigger companies get a bigger say, so the index doesn’t treat its 30 members equally.
Banks are the largest by a distance.
Together, DBS, OCBC and UOB account for more than half of the index.
When half your index sits in one sector, “diversified” starts to look generous.
A synchronised 20% fall in the trio would, on its own, knock about 10% off the STI before a single other stock moved.
What Could Cause Bank Stocks to Crash?
Bank shares don’t crash in a vacuum.
A sharp recession would lift loan defaults and choke loan growth.
Rapid rate cuts would compress net interest margins, dealing a blow to the banks’ bottom lines.
A full-blown financial crisis would layer on credit and liquidity fears.
And regulatory shocks – higher capital requirements or forced dividend restraint – can change the payout picture overnight.
None of these is a forecast.
They’re the switches that, if flipped, would do the damage.
A brief look at some of the most historic crashes paints a similar picture: during the Global Financial Crisis of 2008-2009, the index roughly halved.
During the COVID-19 pandemic, it fell sharply.
Both times, bank shares led the plunge.
Yet dividends continued to be paid, albeit reduced in 2020, and the share prices eventually recovered to new highs.
How Would the STI Be Affected?
Immediately and visibly.
With half the index in three stocks, a bank rout drags the headline number down mechanically, and the gloom rarely stays contained – weak banks sour sentiment across every blue chip, and foreign funds tend to leave together.
But not every constituent falls equally.
Defensives tend to hold up better: Singapore Telecommunications Limited (SGX: Z74) and Sheng Siong Group Ltd (SGX: OV8) both enjoy demand for their critical goods and services that doesn’t vanish in a downturn.
People still buy groceries and use their phones regardless of what loan provisions are doing at DBS.
That’s the case for diversification, made concrete.
Would Dividend Investors Need to Panic?
This is the real worry, because the banks anchor countless income portfolios.
Two things are worth knowing.
First, there’s precedent.
In 2020, the Monetary Authority of Singapore (MAS) capped local banks’ dividends at 60% of the prior year’s payout to preserve capital through COVID – not because the banks were weak, but because the regulator wanted buffers.
Anyone relying solely on bank dividends felt it immediately.
This is where diversification becomes a must to avoid excessive reliance on a single sector.
As mentioned above, owning defensive businesses whose earnings depend on recurring demand – such as grocerie – can cushion the impact of an economic slowdown.
What Long-Term Investors Should Focus On
Don’t confuse price with quality – a falling share price isn’t a broken business.
Check the fundamentals that matter: capital ratios, loan quality, earnings resilience, dividend sustainability, and valuations.
On most of these, Singapore’s banks look sturdy.
The exceptions are worth naming: UOB’s non-performing loan ratio edged up to 1.6% in the second quarter of 2026 (2Q2026), and valuations are elevated (see the table below, figures as of 7 August 2026 unless otherwise stated).
| Metric | DBS | OCBC | UOB |
| Net Profit | S$3.1 billion | S$2.2 billion | S$1.5 billion |
| Return on Equity (ROE) | 17.9% | 14.4% | 9.1% |
| Fully phased-in Common Equity Tier 1 (CET1) ratio | 14.6% | 14.0% | 15.0% |
| Net Interest Margin | 1.87% | 1.70% | 1.74% |
| Non-performing loan ratio | 1.0% | 0.9% | 1.6% |
| Trailing Dividend Yield | 4.2% | 3.5% | 3.8% |
| Dividend Payout ratio (FY2025) | 64.1% | 50.8% | 56.5% |
| Price to Book (P/B) ratio | 3.0x | 2.2x | 1.5x |
And treat corrections as opportunities – businesses earning 11% to 17% on equity rarely go on sale.
The mistakes to avoid are the mirror image: assuming the STI is the banks (it’s half of them, not all), panic-selling a sector-specific dip, ignoring diversification, and fixating on the share price instead of the business behind it.
Get Smart: The STI Is More Than Just the Banks—But the Banks Still Matter
The honest bottom line: yes, a bank-led sell-off would hit the STI hard, because the maths of a cap-weighted index is unforgiving when half your weight sits in one sector.
Pretending otherwise helps no one.
But the STI is not only the banks, and history is emphatic that quality businesses recover from even brutal downturns.
So the useful response to a bank wobble isn’t panic.
It’s to understand how your index is built, check that your own portfolio isn’t secretly 50% banks, and keep a shopping list ready for when good businesses go cheap.
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Disclosure: Wilson H. does not own shares of any companies mentioned.
