Provided is a package for sodium-sulfur batteries in which the inner temperature can be suitably controlled even when it is installed in the place where temperatures and direction of wind change violently. It also includes a box-shaped hollow casing including a base member having a plurality of through-holes and an opening opposing to the base member, for receiving the semiconductor device with the terminals of the semiconductor device inserted into the through-holes. The drain and source regions are doped asymmetrically such that a first charge carrier profile between the channel and drain regions has a steeper slope than a second charge carrier profile between the channel and source regions. The vertical transistor may comprise sequentially formed doped polysilicon layers or doped epitaxial layers. A semiconductor die is mounted over the base substrate with bumps disposed over the first conductive layer. The lower optical waveguide layer has a bandgap which gradually decreases with elevation within the lower optical waveguide layer, and the upper optical waveguide layer has a bandgap which gradually increases with elevation within the upper optical waveguide layer.