We have developed a cost-effective and highly compact 100-Gb/s coarse wavelength division multiplexing (CWDM) transmitter optical subassembly (TOSA) using lens-free hybrid integration. To achieve large alignment tolerances, distributed feedback laser diodes (DFB-LDs) are butt-coupled to a four-channel silica-based planar lightwave circuit (PLC) arrayed waveguide grating, with the silicon sub-mounts and PLC adhesively bonded. Then, a flexible printed circuit is employed to connect the internal DFB-LDs and the exterior of the TOSA package for radiofrequency signal transmission, eliminating the expensive ceramic feed-through. The packaged CWDM TOSA, which is 15.8mm×7.0mm×6.0mm in size, shows a side-mode suppression ratio of >40dB, a 3 dB bandwidth of >18GHz, and error-free transmission with an average optical output power of >0dBm and dynamic extinction ratio of >4.0dB at 25.78125 Gb/s over a 10 km single-mode fiber for all four lanes.