Zinc oxide is a chemical compound with formula ZnO. It is nearly insoluble in water but soluble in acids or alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. It remains white when exposed to hydrogen sulfide or ultraviolet light. Crystalline zinc oxide exhibits the piezoelectric effect, is luminescent, and is light sensitive.

Zinc oxide occurs in nature as the mineral zincite. Zinc peroxide, ZnO₂ .½ H₂O, is a white to yellow powder used in antiseptic ointments.

Zinc white is used as a pigment in paints and is less opaque than lithopone. It is also used as a filler for rubber goods and in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments. Because it absorbs ultraviolet light, zinc oxide can be used in ointments, creams, and lotions to protect against sunburn.

Zinc oxide is a semiconductor with a direct band gap of 3.2 eV (387 nm, deep violet/borderline UV). A common application is in gas sensors. As of 2003, it has been utilized in recent research to build blue LEDs and transparent TFTs.

N-type doped films are often used in thin film technology, where zinc oxide serves as a TCO (transparent conducting oxide). N-type doping is possible by introduction of alumninum or by oxygen defects. Thin-film solar cells, LCD and flat panel displays are typical applications of this material. Zinc oxide is transparent and conductive, and can therefore be used as a transparent electrode. Indium tin oxide (ITO) is another transparent conducting oxide often used in microelectronics.

ZnO layers are mainly deposited by sputtering and chemical vapor deposition (CVD). The latter method allows the growth of a rough layer, which can diffuse the incoming light by scattering, increasing the efficiency of solar cells.