The authors propose and analyze the traveling-wave photodetector (TWPD), an edge-coupled photodetector that is capable of both a larger absolute bandwidth and a larger bandwidth-efficiency product than the waveguide photodetector (WGPD). The intrinsic RC bandwidth limitation is increased in the traveling-wave photodetector by providing for controlled transmission of the electrical wave down the device in parallel with the optical wave and by eliminating bandwidth-limiting electrical reflections. It is shown that 1- mu m wide, parallel-plate, GaAs/AlGaAs, p-i-n TWPD with open-circuit input termination has a 26% greater potential bandwidth-efficiency product than the comparable WGPD, while a TWPD with matched input termination actually has a worse bandwidth-efficiency product than the WGPD. >