A method of forming a compound semiconductor device. The method includes the steps of depositing a film that contains zinc oxide and silicon oxide to contain the zinc oxide by 70 wt % or more on compound semiconductor layer as a diffusion source, and diffusing zinc from the diffusion source into the compound semiconductor layer by annealing. Accordingly, there can be provided a compound semiconductor device manufacturing method containing the step of diffusing zinc into compound semiconductor layers, capable of deepening a Zn diffusion position from a ZnO/SiO2 film to such extent that COD endurance of laser end face window structures can be increased rather than the prior art.