Gallium arsenide epitaxial layers with excellent morphology have been grown by organometallic chemical vapor deposition (OMCVD) on (100) and 2-3° off (100) InP substrates by a modified two-step growth commonly used for GaAs on Si. The layers have been characterized by X-ray diffraction, cross-sectional transmission electron microscopy (TEM), low temperature photoluminescence (PL) and Hall measurements. 1 µm gate GaAs metal-semiconductor field effect transistors (MESFETs) with transconductances as high as 220 mS/mm have been fabricated. These MESFETs have been integrated with buried heterostructure and V-groove InGaAsP lasers. The V-groove laser -MESFET OEIC transmitter has been shown to be capable of direct modulation at 5 Gb/sec bit rate. Finally we have also demonstrated GaAs single quantum well lasers with threshold currents as low as 800 A/cm2for 50 µm wide broad area gain guided devices with 1.25 mm long cavities.