A semiconductor device includes a semiconductor substrate, an isolation structure, and a first electrically conductive structure. The semiconductor substrate has a planar device region and a fin device region. The semiconductor substrate includes a mesa structure disposed in the planar device region and fin-shaped structures disposed in the fin device region. The isolation structure is disposed on the semiconductor substrate and includes a first portion which is disposed on the planar device region and covers a sidewall of the mesa structure, and the isolation structure further includes a second portion which is disposed on the fin device region and located between the fin-shaped structures. The first electrically conductive structure is disposed on the planar device region. The first electrically conductive structure is partly disposed above the mesa structure in a vertical direction and partly disposed above the first portion of the isolation structure in the vertical direction.