Switzerland-based pharmaceutical company Roche has increased its hostile takeover bid for Illumina by 15%, raising its price per share offer to $51.

The move comes after Roche extended its original offer of $44.50 for a second time, moving its deadline to April 20 in order to include an annual meeting that is scheduled to take place on April 18, where Illumina investors could feasibly oust directors and replace them with Roche nominees.

The new offer values Illumina at around $6.6bn, an increase of $900m over the original offer, and comes after Illumina responded strongly to Roche’s extended deadline, deriding the offer as "grossly inadequate".

Illumina’s stance seemed to hold up to scrutiny, as shares in the company continued to trade at approximately 13% above the original bid, indicating that stockholders believed the management’s assertion that Roche had undervalued the company.

Roche’s fresh bid comes as chief executive Severin Schwan slammed Illumina’s management, commenting that the company’s inactivity in takeover proceedings was hurting shareholders.

Roche is now confident that the new bid holds a greater chance of success by representing a premium of 88% over Illumina’s closing stock price on December 21, 2011, the day before takeover rumours first emerged.

In a letter to Illumina CEO Jay Flatley, Roche chairman Franz Humer said, "I strongly hope that you will either agree to commence discussions with us now or remove all obstacles so that your shareholders can make their own determinations about the adequacy of our increased offer."

Illumina have responded to the bid by recommending stockholders to take no action until the proposal had been thoroughly reviewed.