A multichip module of an optical transmitter, which consists of flip-chip bonded 1 x 4 VCSELs on a CMOS driver array IC, is fabricated and demonstrated. The -3 dB bandwidth and adjacent crosstalk of the hybrid integration multichip module are about 4.5 GHz and less than -30 dB, respectively. The whole integrated multichip volume is 1.1 x 1.2 x 0.52 mm(3) for four channels.