This paper presents the results of a stability study of a photodiode realized in the Laboratoire de Métrologie des Rayonnements (LMR-INSAT, Tunisia). The study was performed during six years and concerned with the photodiode optical and electrical characteristics. This study involves in one side, the reflectivity stability for different wavelengths and in the other side, the stability of the series and shunt resistances. The experimental results confirm the stability of the photodiode spectral response since the reflection coefficient maximum uncertainty is equal to 0.0055 with an experimental uncertainty of about 0.0016 (at 1? level) for the mean value of the reflectivity over the study duration. Moreover, the shunt and series resistances are equal to 5.14 k? and 7.61 ? respectively with an uncertainty value of 0.01 k? and 0.04 ? respectively (at 1? level). This photodiode does not display any ageing aspect. Consequently, the PSiZ photodiode can be used as a Transfer Standard for radiometric measurement in the visible spectral range.