A planar dual die package includes a package substrate and first and second semiconductor dice disposed side by side on a first surface of the package substrate. Outer connectors are disposed on a second surface of the package substrate, and the second surface of the package substrate includes a command/address ball region and a data ball region. Each of the first and second semiconductor dice includes die pads disposed in a command/address pad region corresponding to the command/address ball region and in a data pad region corresponding to the data ball region. Each of the first and second semiconductor dice are disposed on the package substrate so that a first direction from the command/address ball region toward the data ball region coincides with a second direction from the command/address pad region toward the data pad region.