We present a gap mirror based monolithic integration technology of functional sections on a gain chip for an external cavity wavelength tunable laser (ECTL). The effective reflectivity and coupling coefficient of the gap mirror can be controlled by changing gap length and gap angle. Utilizing this technique, we experimentally demonstrated full C-band ECTL with integrated variable optical attenuator (VOA). Output power of more than 50 mW with VOA operation, SMSR of more than 50 dB were obtained over the entire C-band