TOKYO, Sept 3 (Reuters) - Japan's Nikkei share average hit a six-month high on Thursday and reached its highest level in three decades in dollar terms, as hopes of more global and domestic economic stimulus boosted sentiment.

Nikkei rose 1.35% to 23,561.01 by midday, its best level since Feb. 21. Converted to dollars, that put the index at its highest since 1990.

"Coronavirus infections are slowing in many parts of the world as various social distancing and hygienic measures have been taken. So clearly, we can say the economy is improving after a brief lull in August," said Nobuhiko Kuramochi, market strategist at Mizuho Securities.

"The Japanese government is likely to extend support for employment and the U.S. yield curve is not pricing in any hike until 2024, prompting investors to buy risk assets," he added.

The broader Topix rose 0.88% to 1,637.75, a six-month high.

Fast Retailing, which has a heavier weighting on the Nikkei compared to Topix, rose 3.7% after reporting strong domestic sales for August.

Semiconductor-related shares also climbed, with Shin-etsu Chemical, manufacturer of semiconductor wafers, rising 4.5% and small motor maker Nidec gaining 2.3%.

Game maker Nintendo rose 0.9% to a 12-year high.

Cable TV operator Sky Perfect JSAT Holdings soared 11.8% after posting a surprise jump in profit, partly due to a fall in costs as the cancellation of various professional sports events led to lower payments for broadcast rights.

SBI Holdings rose 5.2% after a media report said its president discussed a plan to extend a union on regional banks it leads to about 10 banks.

Value shares led the gains with a rise of 1.07%, partly helped by improved sentiment after Warren Buffett's Berkshire Hathaway bought a 5% stake in five Japanese trading houses.

(Reporting by Hideyuki Sano; Editing by Devika Syamnath)