  We implement a technique for measuring the singlet-triplet energy splitting
responsible for spin-to-charge conversion in semiconductor quantum dots. This
method, which requires fast, single-shot charge measurement, reliably extracts
an energy in the limits of both large and small splittings. We perform this
technique on an undoped, accumulation-mode Si/SiGe triple-quantum dot and find
that the measured splitting varies smoothly as a function of confinement gate
biases. Not only does this demonstration prove the value of having an $in~situ$
excited-state measurement technique as part of a standard tune-up procedure, it
also suggests that in typical Si/SiGe quantum dot devices, spin-blockade can be
limited by lateral orbital excitation energy rather than valley splitting.
