ZnS-CHA (CHA = cyclohexylamine) nanocomposite, a unique inorganic organic hybrid semiconductor, has been prepared from a mild solvothermal reaction system. This material contains 2 nm-sized ZnS nanoparticles, and is photoactive toward UV light (<= 300 nm). Under UV-irradiation, the ZnS-CHA nanocomposite is transformed to crystalline zinc hydroxysulfate nanosheets. The driving force of the light-driven transformation reaction is the photogeneration of charges (electrons and holes) in the ZnS nanoparticles, and these photogenerated charges interact with the CHA molecules and the inorganic S2- species, leading to decomposition of the organic component and self-oxidation of the inorganic ZnS nanoparticles to form zinc hydroxysulfate. Through simple thermal treatment, the as-formed zinc hydroxysulfate nanosheets are converted to ultrathin ZnO nanosheets with a porous feature, which exhibit high sensitivity and fast response and recovery for ethanol detection when used as an electrical sensing material.