Measurements down to 10mK of the resistivity, σ, and the ac susceptibility, χac, of the mixed valence alloys Y1-xTmxSe with compositions x=0.01, 0.052, 0.1 and 0.2 are reported. The low T Kondo logarithmic variation of σ is followed at very low T by a saturation or a maximum. χac exhibits a sharp peak at a temperature To proportional to x ( To x=19 mK %Tm). All those effects are characteristic of RKKY interactions between the Tm moments. To is thus interpreted as the spin glass freezing temperature of these moments. Various features of this behavior are briefly discussed. © 1981.