We have developed a technique to generate tunable multi-wavelength picosecond pulses using a self-seeded gain-switched laser diode. The external cavity allows simultaneous feedback of up to four wavelengths into the laser diode for mode selection. A tunable spectral spacing of about 20 nm among the wavelength channels can be obtained. The optimized output side-mode suppression is higher than 20 dB. Different channels in the output are separated temporally and can be individually accessed for modulation. ©1997 American Institute of Physics.