Roche, the Swiss drugs company, today made a $43.7 billion (£22 billion) cash bid for the remaining stake in Genentech, its San Francisco-based partner.

Roche, which owns 55.9 per cent of the cancer drug specialist, said it would pay $89 a share for the remaining stock in Genentech, a 9 per cent premium to the biotech company’s closing price on Friday.

Basel-based Roche made the bid while unveiling a 2 per cent fall in first-half net profit to $5.62 billion, hit by loss of sales of Tamiflu, its influenza drug, and the weak US dollar. Shares in Roche fell down 3.1 per cent.

Roche, which has been a partner with Genentech since 1990, said a combined entity would generate more than $15 billion in annual revenue and employ a total of about 25,000 people in the US.

The company did not specify how many of Genentech's 10,700 employees would be retained.

Roche expects to generate annual pre-tax cost benefits of between $750 million and $850 million and to add to earnings per share in the first year.

Franz Humer, chairman at Roche, said a takeover would improve operational efficiency by reducing complexity, eliminating duplications and increasing scale in the US.

"Combining the strengths of Roche and Genentech will create significant value and result in benefits for patients, employees and shareholders," he said.

Roche said Genentech's San Francisco site would operate as an independent research and early development centre and become the headquarters of the combined US commercial operations.

Roche said the Genentech board would establish a committee of independent directors to evaluate Roche's proposal with the assistance of independent outside financial and legal advisers. Genentech board members who are employees of Roche will not participate in the evaluation.

Roche plans a cash merger but did not specify exactly how the deal would be conducted or funded.

Precise terms would be determined through negotiations with the independent directors, Roche said. "Roche expects to complete the transaction as soon as possible following negotiation of a definitive merger agreement," the company's statement said.

Analysts said Roche was taking advantage of a weak US dollar and a recent return to the sector by investors worried about financial stocks amid the current global economic gloom.

The Genentech bid is the latest in a string of acquisitions of biotech assets by large pharmaceutical companies keen to fill sparse new product pipelines.

Roche would gain control of all revenues for big-selling Genentech cancer drugs Avastin and Herceptin, as well as absorbing a portfolio of new medicines.

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