Abstract: A specific IC layout structure for the MOSFET having a narrow and short channel, especially when the width and the length of the channel are both as small as 1 micron or less, is disclosed. In the IC layout structure, a mask includes a first mask region for defining a first active region, a second mask region for defining a second active region, and a third mask region for defining a channel region, and the third mask region is connected to the first and the second mask regions, respectively. An angle at an joint between the first mask region and the third mask region and/or an angle at an joint between the second mask region and the third mask region are/is greater than 90 degrees so that there is more space beside the channel region provided for the growth of the field oxide. Thus a 3-D oxidation thinning effect can be prevented and the properties of the MOSFET having a narrow and short channel can be stabilized.