A method of producing a semiconductor device adapted for mounting on a wiring board comprising the steps of: forming an insulation layer by stacking a plurality of resin layers on a surface of a semiconductor substrate excluding scribe lines separating adjacent semiconductor chip regions, forming an electronic circuit on the surface of the substrate or buried in the insulation layer, and forming a wiring layer electrically connected to the electronic circuit and buried in the insulation layer; forming a conductive post on the insulation layer and electrically connected to the wiring layer; forming an insulating buffer layer, adapted to buffer a stress which is generated when the semiconductor device is mounted on a wiring board, on the insulation layer; and dicing the substrate on the scribe lines; wherein in the step of forming the buffer layer: the buffer layer is formed by a printing method using a printing mask (MK,SC) and a pressurized squeegee, the printing mask comprising a mesh screen having a thickness of 10μm or less and a metal mask having a thickness corresponding to a thickness of the buffer layer, the mask containing a plurality of first portions spreading in a first direction and a plurality of second portions spreading in a second direction orthogonal to the first direction, said first and second portions being aligned along the scribe lines and being in contact with the upper resin layer, and the squeegee is slid on the printing mask (MK,SC) in a direction crossing at 45° to the directions of the first and the second mask portions, whereby the insulating buffer layer is formed on the insulation layer and covers the conductive post. forming an insulation layer by stacking a plurality of resin layers on a surface of a semiconductor substrate excluding scribe lines separating adjacent semiconductor chip regions, forming an electronic circuit on the surface of the substrate or buried in the insulation layer, and forming a wiring layer electrically connected to the electronic circuit and buried in the insulation layer; forming a conductive post on the insulation layer and electrically connected to the wiring layer; forming an insulating buffer layer, adapted to buffer a stress which is generated when the semiconductor device is mounted on a wiring board, on the insulation layer; and dicing the substrate on the scribe lines; wherein in the step of forming the buffer layer: the buffer layer is formed by a printing method using a printing mask (MK,SC) and a pressurized squeegee, the printing mask comprising a mesh screen having a thickness of 10μm or less and a metal mask having a thickness corresponding to a thickness of the buffer layer, the mask containing a plurality of first portions spreading in a first direction and a plurality of second portions spreading in a second direction orthogonal to the first direction, said first and second portions being aligned along the scribe lines and being in contact with the upper resin layer, and the squeegee is slid on the printing mask (MK,SC) in a direction crossing at 45° to the directions of the first and the second mask portions, whereby the insulating buffer layer is formed on the insulation layer and covers the conductive post. the buffer layer is formed by a printing method using a printing mask (MK,SC) and a pressurized squeegee, the printing mask comprising a mesh screen having a thickness of 10μm or less and a metal mask having a thickness corresponding to a thickness of the buffer layer, the mask containing a plurality of first portions spreading in a first direction and a plurality of second portions spreading in a second direction orthogonal to the first direction, said first and second portions being aligned along the scribe lines and being in contact with the upper resin layer, and the squeegee is slid on the printing mask (MK,SC) in a direction crossing at 45° to the directions of the first and the second mask portions, whereby the insulating buffer layer is formed on the insulation layer and covers the conductive post.