  We describe a measurement method that enables the correct estimation of the
charging energy of an unintentional quantum dot (QD) in the channel of a
metal-oxide-semiconductor field-effect transistor (MOSFET). If the channel has
a dominant QD with a large charging energy and an array of stray QDs with much
weaker charging, this method eliminates the additional voltage drops due to
stray QDs by regarding the stray QDs as series resistors. We apply this method
to a short-channel MOSFET and find that the charging energy of the dominant QD
can indeed be smaller than the size of the Coulomb diamond.
