COLOMBO, July 13 (Reuters) - Sri Lankan shares ended slightly higher in thin trade on Wednesday, extending gains from the previous session when it touched a near three-week closing high, as investors bought into banking stocks.

Sentiment was also boosted after Sri Lanka raised $1.5 billion in its first sale of dual-tranche eurobonds earlier this week, as the $6.6 billion in offers for the issue showed global investors were bullish about the prospects of the $82 billion economy.

The benchmark Colombo stock index rose slightly for the sixth straight day, and ended up 0.02 percent at 6,402.78, its highest close since June 22. It gained 1.3 percent last week in its first weekly gain in four.

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"Sentiment has improved and investors' mindset have changed. Positive sentiment has emerged," said Dimantha Mathew, head of research, First Capital Equities (Pvt) Ltd.

After the bond deal yields in local T-bill auction fell with 364-day T-bill rates fell at Wednesday's auction for the first time since April 15.

Turnover stood at 1.53 billion rupees ($10.47 million), its highest since May 18 and well above this year's daily average of around 740.2 million rupees.

Overseas investors, who have offloaded shares worth a net 5.08 billion rupees so far this year, bought equities worth a net 211.9 million rupees on Wednesday.

Shares stumbled recently and hit their lowest close since April 7 on Monday, after losing in 10 of 11 trading sessions, on worries over capital gains tax on stocks, high-interest rates and policy uncertainty.

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Shares in Aitken Spence Plc gained as much as 5.11 percent while Hemas Holdings Plc climbed as much as 2.33 percent and the biggest-listed lender Commercial Bank of Ceylon Plc rose as much as 1.09 percent.

Top telecom operator Dialog Axiata PLC gained as much 0.93 percent after announcing the leadership succession plan on Tuesday.

($1 = 146.0000 Sri Lankan rupees) (Reporting by Ranga Sirilal and Shihar Aneez; Editing by Sherry Jacob-Phillips)