A power semiconductor device, comprising: a disc-shaped first electrode having a first contact face and a disc-shaped second electrode having a second contact face opposite to the first contact face; a wafer sandwiched between the first electrode and the second electrode; an outer insulating ring attached to the first electrode and to the second electrode, the outer insulating ring surrounding the wafer; an inner insulating ring (42; 42') inside of the outer insulating ring and surrounding the wafer; a ring-shaped first flange portion laterally surrounding a main portion of the first electrode, a radial first direction being parallel to the first contact face; an O-ring radially surrounding the main portion of the first electrode and being sandwiched in a second direction perpendicular to the first contact face between the inner insulating ring (42; 42') and the first flange portion, wherein the O-ring has in a relaxed state a cross-section being elongated in a vertical direction perpendicular to the radial direction, such that in a relaxed state, a height of the O-ring in the vertical direction is greater than a width of the O-ring in the radial direction, and wherein the O-ring is resiliently reversibly deformable; wherein the first electrode has a second flange portion radially extending from the main portion of the first electrode on a side of the first flange portion opposite to the O-ring, wherein the second flange portion is an integral part of the first electrode; and wherein in an orthogonal projection onto a plane parallel to the first contact face, the first flange portion overlaps the second flange portion in an area radially extending between the O-ring and the main portion of the first electrode. a disc-shaped first electrode having a first contact face and a disc-shaped second electrode having a second contact face opposite to the first contact face; a wafer sandwiched between the first electrode and the second electrode; an outer insulating ring attached to the first electrode and to the second electrode, the outer insulating ring surrounding the wafer; an inner insulating ring (42; 42') inside of the outer insulating ring and surrounding the wafer; a ring-shaped first flange portion laterally surrounding a main portion of the first electrode, a radial first direction being parallel to the first contact face; an O-ring radially surrounding the main portion of the first electrode and being sandwiched in a second direction perpendicular to the first contact face between the inner insulating ring (42; 42') and the first flange portion, wherein the O-ring has in a relaxed state a cross-section being elongated in a vertical direction perpendicular to the radial direction, such that in a relaxed state, a height of the O-ring in the vertical direction is greater than a width of the O-ring in the radial direction, and wherein the O-ring is resiliently reversibly deformable; wherein the first electrode has a second flange portion radially extending from the main portion of the first electrode on a side of the first flange portion opposite to the O-ring, wherein the second flange portion is an integral part of the first electrode; and wherein in an orthogonal projection onto a plane parallel to the first contact face, the first flange portion overlaps the second flange portion in an area radially extending between the O-ring and the main portion of the first electrode.