A strengthened window-type semiconductor package is provided. A substrate having an opening is mounted with at least a chip in a manner that, an active surface of the chip covers and partly exposed to the opening, and electrically connected to the substrate by bonding wires formed through the opening. An elastic non-conductive material is applied over the chip exclusive of the active surface. An upper encapsulant is formed to encapsulate the chip and the non-conductive material, and a lower encapsulant is formed to encapsulate the bonding wires and seal the opening. With provision of the non-conductive material for encapsulating the chip before forming the upper encapsulant, the chip can be prevented from cracking particularly at corner and edge positions that encounter relatively greater thermal stress during subsequent fabrication processes such as curing of the upper encapsulant and thermal cycles.