The novel results reported in this paper pertain to the behavior of the moderate‐to‐low frequency reactance of Si and GaAsp‐njunction diodes as a function of the incident photon flux densityF. We have observed that the diode reactance, which is invariably capacitive under dark or low photon flux conditions, may turn inductive at a threshold photon flux densityFthdepending on the diode structure and the spectral characteristics of the incident radiation. Photoinductance values of greater than 100 &mgr;H/cm2were measured reproducibly at room temperature using a 1‐MHz signal in severalp+p‐n,n+‐p, andn+n‐pp+type Si diodes (dc open‐circuited) illuminated with argon ion (4880 A˚), He‐Ne (6328 A˚) lasers, and white light radiation sources operating at moderate‐to‐high photon flux densities. Specifically, the photon flux density was varied from virtually dark to about 20 times more intense as compared to the solar flux at air massm=2. Theoretically, an explicit inductive component is shown to originate in the conductivity modulated sectionlcmnof the base region when the photogenerated minority carrier concentration becomes comparable to that of majority carriers. The magnitude of photoinductive reactance is computed as a function of incident photon flux densityFand results are compared with experiment for an+‐pSi cell.