Amgen Inc. is the world's biggest biotech company. It has offered to acquire biotech Onyx Pharmaceuticals. The deal was priced at US$120 per share piece in cash. This was reported by the Canadian newspaper, Financial Post on Friday. The shares of Onyx rose up to 30% after hours trading.

The newspaper stated that the documents it has seen said that Amgen sent a proposal to Onyx. The proposal contained interest to acquire the company which is worth US$10 billion in cash. Amgen requested due diligence and a document review period for the deal.

The document was sent about two weeks ago according to the Financial Post. The two firms are based in California. Amgen had reached sales of US$17.3 billion in 2012. Onyx brought in revenue of US$362 million.

Big biotech companies have become acquirers of smaller biotech firms. This was after their stocks have run up. In addition, larger biotech firms have low interest rates making them bankroll their drug development.