The　semiconductor-electrolyte　interface　dominates　the　behaviours　of　semiconductor　electrocatalysis,　which　has　been　modelled　as　a　Schottky-analogue　junction　according　to　classical　electron　transfer　theories.　However,　this　model　cannot　be　used　to　explain　the　extremely　high　carrier　accumulations　in　ultrathin　semiconductor　catalysis　observed　in　our　work.　Inspired　by　the　recently　developed　ion-controlled　electronics,　we　revisit　the　semiconductor-electrolyte　interface　and　unravel　a　universal　self-gating　phenomenon　through　microcell-based　in　situ　electronic/electrochemical　measurements　to　clarify　the　electronic-conduction　modulation　of　semiconductors　during　the　electrocatalytic　reaction.　We　then　demonstrate　that　the　type　of　semiconductor　catalyst　strongly　correlates　with　their　electrocatalysis;　that　is,　n-type　semiconductor　catalysts　favour　cathodic　reactions　such　as　the　hydrogen　evolution　reaction,　p-type　ones　prefer　anodic　reactions　such　as　the　oxygen　evolution　reaction　and　bipolar　ones　tend　to　perform　both　anodic　and　cathodic　reactions.　Our　study　provides　new　insight　into　the　electronic　origin　of　the　semiconductor-electrolyte　interface　during　electrocatalysis,　paving　the　way　for　designing　high-performance　semiconductor　catalysts.