Alkyl group modified hyper branched poly(alkoxysiloxane)s (PAOS) were synthesized via a one‐pot co‐monomer route based on a non‐aqueous condensation reaction. By using tri(ethoxyalkylsilane) as co‐monomer we are able to introduce a high amount of alkyl groups into the PAOS molecule. The chemical structure and degree of modification were analyzed by 29Si‐NMR and GPC. According to thermal gravimetric analysis (TGA) the conversion of PAOS to silica is highly affected by type and the content of the modifying units. With increasing of both the chain length and the quantity of alkyl groups the rate of conversion of PAOS to silica is decreased. Additionally, we discuss the influence of atmosphere and temperature on the degree of conversion to silica within a defined time.