Field effect transistor and method of manufacturing the same

A field-effect transistor comprising:

• a substrate;
• a first semiconductor layer including a plurality of semiconductor layers stacked on said substrate, and including a channel;
• a source electrode and a drain electrode which are formed on said first semiconductor layer;
• a gate electrode;
• and
• a second semiconductor layer formed on said first semiconductor layer and below said gate electrode, said second semiconductor layer having a conductivity type opposite to a conductivity type of the channel, wherein:
• said first semiconductor layer has a containing region which contains first impurities, and a non-containing region which does not contain the first impurities,
• said containing region includes a first region, the first region is defined by a vicinity region of a portion of an interface between the containing region and the non-containing region,
• said second semiconductor layer includes a second region, the second region is located directly above the first region,
• a concentration of the first impurities of the second region is lower than a concentration of the first impurities of the first region, and
• both of said first region and said second region are located directly below an end portion of said gate electrode.