By Kevin Buckland
TOKYO, Aug 13 (Reuters) - Japan's Nikkei share average breached the 43,000-mark for the first time on Wednesday, with the broader Topix index also scaling a fresh all-time peak, tracking Wall Street's overnight gains and extending the rally to a sixth straight session.
The Nikkei .N225 gained as much as 1.7% to touch an unprecedented 43,451.46 before ending the day at a record-high closing level of 43,274.67.
That took its winning run to 7.4% since August 4. Monday of this week was a national holiday in Japan.
The broader Topix .TOPX advanced as much as 1.2% to a record 3,103.31 points, before finishing at 3,091.91 - also booking a sixth-straight session of gains.
Overnight, the S&P 500 .SPX and Nasdaq .IXIC ended at record highs as a moderate reading of July inflation bolstered bets for a Federal Reserve interest rate cut next month. .N
"A sense of relief is permeating through markets" following the U.S. Consumer Price Index (CPI) data, leading Japanese stocks "to take a step higher," said Maki Sawada, an equities strategist at Nomura Securities.
At the same time, "there are signs that the Nikkei is overheated after its extremely steep rally, and a steep drop at any time wouldn't come as any surprise," she added.
The Nikkei's relative strength index (RSI) rose above 75, well beyond the 70 line that many analysts consider indicative of an overheated market. The RSI was at a similar level on July 24, and the Nikkei fell in the following four sessions.
Of the Nikkei's 225 components, 151 rose versus 74 that fell.
Tech shares stood out, with chipmaker Renesas Electronics 6723.T jumping almost 7%, chip-testing equipment maker Advantest 6857.T rising 5.4% and Sony Group 6758.T gaining 3.5%.
A strong earnings season continued to power big advances for some stocks, with tyre maker Yokohama Rubber 5101.T vaulting 8.3% to be the Nikkei's biggest percentage gainer.
Athletic apparel company Asics 7936.T soared nearly 18% after its favorable financial results to be the best-performing Topix stock.