Monolithically integrated electroabsorption modulated lasers (EML) are widely being used in the optical fiber communication systems, due to their low chip, compact size and good compatible with the current communication systems. In this paper, we investigated the effect of Zinc diffusion on extinction ratio of electroabsorption modulator (EAM) integrated with distributed feedback laser (DFB). EML was fabricated by selective area growth (SAG) technology. The MQW structure of different quantum energy levels was grown on n-type InP buffer layer with 150nm thick SiO2 parallel stripes mask by selective area metal-organic chemical vapor deposition (MOCVD). A 35nm photoluminescence wavelength variation was observed between the laser area (λPL=1535nm) and modulator area (λPL=1500nm) by adjusting the dimension of parallel stripes. The grating (λ=1550nm) was fabricated in the selective area. The device was mesa ridge structure, which was constituted of the DFB laser, isolation gap and modulator. The length of every part is 300μm, 50μm, and 150μm respectively. Two samples were fabricated with the same structure and different p-type Zn-doped concentration, the extinction ratio of heavy Zn-doped device is 12.5dB at -6V. In contrast, the extinction ratio of light Zn-doped device is 20dB at -6V, that was improved for approximate 60%. The different Zn diffusion depth into the MQW absorption layer was observed by Secondary ion mass spectrometer (SIMS). The heavy Zn-doped device diffused into absorption layer deeper than the light Zn-doped device, which caused the large non-uniformity of the electric field in the MQW layer. So the extinction ratio characteristics can be improved by optimizing the Zn-doped concentration of p-type layer.