TOKYO, Feb 26 (Reuters) - Japanese shares slumped on Friday, logging their biggest daily decline in nearly a year, after a spike in global bond yields spooked investors already uneasy about the market's stretched valuation.

The Nikkei average ended down 3.99% at 28,966.01, hitting its lowest level in almost three weeks. The broader Topix fell 3.21% to 1,864.49. Both indexes posted their biggest single-day fall since April last year.

All of the Tokyo Stock Exchange's 33 industry subindexes were in the red, with electronic machinery makers, pharmaceuticals and real estate companies falling more than 3%.

Semiconductor-related shares, one of the main leaders of the market's rally to 30-year highs, succumbed to heavy selling, after U.S. chip shares fell 5.8%.

Sumco fell 5.59%, while Lasertec shed 5.33%. Advantest dropped 7.51%, while Screen Holdings lost 6.53%.

Precautions about rising inflation and a weak U.S. bond auction boosted global bond yields, dampening investors' appetite for risk assets.

Analysts pointed to market's sharp rise as contributing to its current slide as well. "In a nutshell, I think the stock market had risen a bit too much," said Soichiro Monji, chief strategist at Nishimura Securities.

Rising bond yields also hit assets that have been considered as an alternative to low-yielding bonds. The TSE's index of real estate investment trusts (REITs) fell 2.84%

Market players are now awaiting whether the Bank of Japan, which has refrained from buying stock exchange traded funds (ETFs) so far this month, will purchase them later in the day.

The central bank in its next policy meeting is expected to signal it will make its ETF purchases more flexible. (Reporting by Hideyuki Sano and Stanley White; Editing by Vinay Dwivedi)