In the present study the very fast high;temperature thermal decomposition of silane was used as a Si atom source to initiate its reactions with either CO or CO2. The experiments were performed behind reflected shock waves by applying atomic resonance absorption spectroscopy (ARAS) for detecting Si and C atoms. In the first part initial mixtures of 0.75-20 ppm SiH4 and 0.2-5% CO in Ar were used to perform experiments in the temperature range 2720 K less than or equal to T less than or equal to 5190 K at pressures 0.6 bar less than or equal to p less than or equal to 1.0 bar. From the measured Si atom absorption profiles the rate coefficient for the reaction Si + CO --> (k3) SiO + C (R3) was determined by applying the first-order method. The results were summarized by the following Arrhenius expression : k(3) = 7.8 X 10(14) exp(-34510K/T) cm(3) mol(-1) s(-1) +/- 20% The evaluation of measured dopes of C atom formation results in rate coefficients k(3) close to the values found from Si atom measurements. This demonstrates SiO and C to be the dominant products. In the second part Si atom measurements in SiH4/CO2/Ar mixtures were performed to study its reaction with CO2. Initial mixtures of 0.5-0.75 ppm SiH4 and 200 ppm CO2 were used to carry out experiments in the temperature range 2100 K less than or equal to T less than or equal to 3160 K at pressures 0.4 bar less than or equal to p less than or equal to 1.4 bar. From the Si atom concentration profiles the rate coefficient of the reaction Si + CO2 --> (k4) SiO + CO (R4) was determined by applying again the first-order method. The results of the data interpretation can be summarized by the following Arrhenius expression : k(4) = 6.0 X 10(14) exp(-9420K/T) cm(3) mol(-1) s(-1) +/- 25% Although it was not possible to observe any reaction product, the formation of SiO and CO is obviously reasonable due to energetic reasons.B널