  Electromagnetic form factors serve to explore the intrinsic structure of
nucleons and their strangeness partners. With electron scattering at low
energies the electromagnetic moments and radii of nucleons can be deduced. The
corresponding experiments for hyperons are limited because of the unstable
nature of the hyperons. Only for one process this turns to an advantage: the
decay of the neutral Sigma hyperon to a Lambda hyperon and a real or virtual
photon. Due to limited phase space the effects caused by the Sigma-to-Lambda
transition form factors compete with the QED radiative corrections for the
decay $\Sigma^0\to\Lambda e^+e^-$. These QED corrections are addressed in the
present work, evaluated beyond the soft-photon approximation, i.e., over the
whole range of the Dalitz plot and with no restrictions on the energy of the
radiative photon.
