Recently, it has been shown that when a semiconductor laser is directly modulated at high frequencies, the modulation signals suffer substantial loss and phase shift propagating from the wire feed point along the length of the laser. It was suggested that these distributed microwave effects lead to a further bandwidth degradation in electrical current injection over the single‐pole roll‐off predicted by a lumped RC model. We show, however, that this degradation is significant only when the laser is driven directly by a voltage source. In contrast, when the laser is driven, commonly, through a 50 Ω transmission line the degradation is minimal, and the total injection current is still RC limited. © 1995 American Institute of Physics.