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 (R) 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 (Z) 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 (Z) perpendicular to the radial direction (R), 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 (R) 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 (Z) 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 (Z) perpendicular to the radial direction (R), 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 . <EOS>