The phenomena of electron injection occurring during anodic dissolution of Si are studied in a dual-electrolyte transistor-like geometry : variations in the population of minority carriers of a p-Si wafer resulting from injection are detected by a second liquid junction on the back side of the electrode. Investigations in acidic fluoride media show that electrons injected during porous silicon formation undergo ready surface recombination. A significant back current is detected in the electropolishing regime, indicating that important injection processes occur even under the latter conditions. Analogous investigations at p-Si in 2 M KOH show electron injection in correspondence to the oxidation peak leading to passivation. Results are compared with literature data and discussed with reference to current models of silicon dissolution.