Semiconductor device

A transistor, comprising:

• a substrate;
• an isolation structure disposed in the substrate;
• a well region laterally extending in a closed path along an inner sidewall of the isolation structure, wherein a portion of the substrate is surrounded by an inner sidewall of the well region to form a native region and the native region has a doping concentration substantially equal to a doping concentration of the substrate;
• and
• a gate structure disposed over the substrate and across the inner sidewall of the isolation structure.

A semiconductor device, comprising:

• a substrate;
• a first native transistor comprising a first isolation structure and a first well region laterally extending along an inner sidewall of the first isolation structure, wherein a first portion of the substrate is surrounded by an inner sidewall of the first well region to form a first native region, and the first well region has the same conductivity type with the substrate;
• and
• a second native transistor comprising a second isolation structure and a second well region laterally extending along an inner sidewall of the second isolation structure, wherein a second portion of the substrate is surrounded by an inner sidewall of the second well region to form a second native region, and the second well region has the same conductivity type with the substrate,
• wherein an area of the first native region is different from an area of the second native region,
• wherein a doping concentration of the first and second native regions is substantially equal to a doping concentration of the substrate.