The first demonstration of a directly modulated microring laser array is presented for ON-OFF keyed, wavelength- division-multiplexed fiber-optic data transmission. GaInAsP–InP microring resonators oscillating at separate wavelengths in the 1.5-m band are vertically coupled to a common passive wave-guide bus, which is fabricated on the reverse side of the InP membrane. Two microrings defined with radii for a wavelength channel separation of 6 nm have been assessed for both individual and simultaneous operation. Negligible power penalty (0.2 dB ) is observed for wavelength-division-multiplexed operation with and without transmission over a 25-km fiber span in a manner which indicates low crosstalk between the integrated sources. A device area of less than 0.12 mm per microring on a common passive bus allows a highly scalable solution for short-reach wavelength-multiplexed links.