We determine the locations of unintentional quantum dots (U-QDs) in a silicon nanowire with a precision of a few nanometers by comparing the capacitances to multiple gates with a capacitance simulation. Given that we observe U-QDs in the same location of the wire in multiple devices, their cause is likely to be an unintended consequence of the fabrication, rather than of random atomic-scale defects as is typically assumed. The locations of the U-QDs appear to be consistent with conduction band modulation from strain from the oxide and the gates. This allows us to suggest methods to reduce the frequency of U-QDs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692387]