A method of manufacturing a transistor in a semiconductor device, comprising the steps of:
- providing a semiconductor substrate in which a well is formed in an active region and an isolation film is formed in an isolation region;
- forming low-concentration impurity regions in source/drain regions of the semiconductor substrate;
- forming trenches in the semiconductor substrate of the low-concentration impurity regions so that the trenches are adjacent to the isolation film;
- sequentially forming a gate oxide film and a gate on the semiconductor substrate between the trenches;
- and
- forming high-concentration impurity regions at the bottoms of the trenches to form source/drain consisting of the low-concentration impurity regions and the high-concentration impurity regions.