Several designs of micro-fabricated PCR-chips made in silicon have been developed. Upon miniaturization the surface-to-volume ratio (SVR) increases and therefore, effects related to the non-specific adsorption of Taq DNA polymerase and template DNA to chip-surfaces become significant.To repress the surface-mediated inhibition of these biological macro-molecules: (1) the PCR-compatibility of SiO x -surfaces, (2) the combination of silanization and dynamic coating with BSA on SiO x -surfaces on the PCR-efficiency, and (3) the stability of these surface-passivating films during PCR were investigated off-chip. (4) Finally, on-chip PCR-experiments were carried out under optimized reaction conditions.(CH 3 ) 3 SiCl, (CH 2 ) 2 SiCl 2 , [(CH 3 ) 3 Si 2 ]NH and CH 3 (CH 2 ) 2 SiCl 3 were used to passivate SiO x -surfaces. The PCR was performed according to published procedures and the yield of the PCR-products was determined by gel electrophoresis analysis. To follow the degradation of the surface-passivating films contact angles were measured. It could be demonstrated that: (1) SiO x -surfaces were an inhibitor of the PCR; (2) the PCR-efficiency of silanized SiO x -surfaces was in the order: CH 3 (CH 2 ) 2 SiCl 3 ~(CH 3 ) 2 SiCl 2 >CH 3 SiCl 3 >[(CH 3 ) 3 Si 2 ]NH and the amount of PCR-products was reduced from run to run; (3) the stability of the surface-passivating films resembled the same trend and none of these surfaces were stable for more than three consecutive PCR runs; (4) the specificity and product yield of the on-chip PCR was found to be equivalent to a conventional one, using a (CH 3 ) 2 SiCl 2 -modified PCR-chip with a power consumption of 2.7W, heating (cooling) rates of up to 50Ks - 1 (4) and reaction volumes in the range of 1-4μl.Based on this test configuration the silanization of SiO x -surfaces alone will not be suited for multiple or long-term applications due to the degradation of the surface-passivating films.