Interaction between GeR4 complexes with partially dehydroxylated silica surfaces has been studied by infrared spectroscopy, C-13 CP-MAS NMR, and analytical methods. The tetraalkylgermanium complexes are physisorbed, at room temperature : a hydrogen-type bonding occurs between the terminal methyl group of the alkyl ligands and the surface silanol groups. The results obtained for the two complexes (R=Et, n-Bu) and for two supports (silica(200) and silica(500)) are rather similar and may be explained by a simple reaction between the surface silanols and the tetraalkylgermanium compounds : =Si-O-H + GeR4 --> =Si-O-GeR3 + RH. Surprisingly, thermal treatment under vacuum (10(-4) Torr) of the well-defined =Si-O-GeR3 complex supported on silica(200) and silica(500) does not lead to any evolution of gas between 200 and 400-degrees-C. The stabilility of the grafted complex is also evidenced by analytical data and by infrared spectroscopy. The extraordinary thermal stability of =Si-O-GeR3 is compatible with the higher stability of germanium alkyl complexes as compared with the tin ones. A mechanism of decomposition of the surface alkyl complexes is proposed.