The upper subsidiary diffuse resonances were first observed in the ionosphere in the Alouette 2 topside sounder experiment, later by the ISIS 1 satellite, and then by the JIKIKEN (EXOS B) satellite during its electron injection experiment. The frequencies of the subsidiary resonanaces are just higher than those of the diffuse resonances Dn (n=1,2,3,4). In our work we identify the upper subsidiary diffuse resonance as a hybrid resonance of the diffuse and cyclotron resonances. The corresponding frequencies are fT,Dn= (f2Dn+f2H)1/2,n=1,2,3,4⋅⋅⋅, where fT,Dn is the observed frequency of the nth upper subsidiary diffuse resonance, fDn is the frequency of the nth diffuse resonance, and fH is the electron gyrofrequency. ¿ American Geophysical Union 1989