A method of forming thick and thin gate oxides comprising the following steps. A silicon semiconductor substrate having first and second active areas separated by shallow isolation trench regions is provided. Oxide growth is selectively formed over the first active area by UV oxidation to form a first gate oxide layer having a first predetermined thickness. The first and second active areas are then simultaneously oxidized whereby the first predetermined thickness of the first gate oxide layer is increased to a second predetermined thickness and a second gate oxide layer having a predetermined thickness is formed in the second active area. The second predetermined thickness of the first oxide layer in the first active area is greater than the predetermined thickness of the second oxide layer in the second active area.