A packaged semiconductor device has, according to one embodiment of the present invention, a semiconductor pellet having an electronic circuit therein and electrode pads formed on a principal surface of the pellet, a plurality of electrical connection bumps provided on the electrode pads, a plurality of heat dissipation bumps provided at the principal surface of the pellet and electrically insulated from the electronic circuit and the electrode pads, electrical connection leads for the electronic circuit, heat dissipators for the electronic circuit and a packaging material for sealing pellet, the electrical connection bumps, the heat dissipation bumps and parts of the electrical connection leads and the heat dissipator. One or more of the heat dissipation bumps are arranged relatively nearer to the electronic circuit than the electrical connection bumps for thermal coupling to the electronic circuit. One or more of the electrical connection leads may be engaged with the electrical connection bumps and the heat dissipation bumps and/or one or more of the dissipators may be engaged with the heat dissipation bumps and the electrical connection bumps, thereby serving to effect electrical connection to and heat dissipation for the electronic circuit.