Initially non-conducting gas is ionized by a thin viscous shock wave. Upstream there can be no magnetohydrodynamic interaction because of the zero conductivity, but the conducting downstream region may have a magneticStructure which interacts with the flow variables. A theoretical analysis is made in the zeromagnetic-Prandtl-number (‘non-viscous ’) limit, i.e. ohmic dissipation is the dominant diffusion mechanism. Unlike magnetohydrodynamic shocks in a pre-ionized gas, ionizing shock waves are not necessarily plane-polarized. Thus ‘skew ’ shock structures can exist, in which the upstream and downstream magnetic field vectors and the shock wave normal do not all lie in a single plane. Explicit solutions are given for typical values of the governing parameters, showing how the magnetic field vector rotates about the shock wave normal as its transverse component changes in magnitude through the shock layer. Skew shocks are necessarily sub-Alfvénic downstream. Unlike the pre-ionized case, the range of trans-Alfvénic shock waves is not excluded, since these shocks can absorb Alfvén waves within their structure. With strong magnetic fields it is possible to achieve very high downstream temperatures by Joule heating. Alternatively, in some cases, magnetic energy can be fed into directed kinetic energy, producing an overall expansion shock.