In order to obtain information about the nuclear transitions that produce fission‐fragment x rays, the yield ofKx rays emitted in the thermal‐neutron fission of U235was measured as a function of the time after fission for times between 1 and 60 nsec, as a function of the mass of the fragment emitting the x ray, and as a function of the total kinetic energy of the fragment pair emitting the x ray. Three‐parameter data were recorded event by event. Two of the parameters contained information about the energies of the fission fragments from which it was possible to calculate the mass of each fragment. The third parameter contained information from which the elapsed time between the detection of one of the fission fragments and the detection of the x ray could be calculated. The results are compared with previously reported results for Cf252and U235. There appears to be little difference between the Cf252and U235x‐ray yields per fragment. A sufficient understanding of the mechanisms responsible for x‐ray emission would permit the independent yield distributions of nuclides produced in fission to be obtained from measured x‐ray yields.