Japan's key benchmark stock index edged up to a one year-high, supported by gains for the phrama sector thanks to drugmaker Eisai rallying hard, though weak chip-related stocks capped the gains after disappointing results from Texas Instruments.

The benchmark Nikkei average added 0.3% to 22,625.38, its highest finish since October last year, while the broader Topix advanced 0.6% to a 10-1/2-month closing peak at 1,638.14.

Tokyo-listed semiconductor-related shares were hit hard, with Rohm, Renesas Electronics and Tokyo Electron sliding 4.1%, 5.3% and 4.1%, respectively, as Texas Instruments slumped nearly 10% in after-hour trading overnight.

The leading American chip designer on Tuesday forecast current-quarter revenue well below estimates, in a fresh sign that the global microchip industry is being squeezed by a downturn in demand as well as a prolonged US-China trade dispute.

The Nikkei heavyweight Softbank Group shed 2.5% as the tech conglomerate agreed to spend $10 billion to take over US office-space sharing startup WeWork on Tuesday, doubling down on an ill-fated investment and paying off its co-founder Adam Neumann to relinquish control.

Drugmaker Eisai soared 18.1% to its daily-limit high after its partner Biogen revived plans on Tuesday to seek US approval for Alzheimer's treatment aducanumab, which surprised investors and sent the US pharma firm's share up 27% overnight.

The pharmaceutical sector jumped 2.4%, helped by Eisai's big gains, to become the second best performers among the Tokyo bourse's 33 sector subindexes. Sumitomo Chemical dropped 3.2% after the company slashed its operating profit forecast for the year through March by 10.5% to 170 billion yen ($1.6 billion). Japan's mid-year earnings season kicks off this week, with electric-motor maker NIDEC's results coming after the market close on Wednesday.