In this paper a new integrated optical chip containing silica-on-silicon waveguides end-fire coupled to micromachined silicon mesa photodiodes is presented. Contrary to similar devices presented in the literature, buried waveguide structures with a total glass thickness of 15 micrometer have been used, which has considerable potential for new and interesting applications. Unlike the conventional surface-illuminated photodiode, the light is coupled in parallel to the junction in these devices. This configuration results in several advantages, two of which are improved spectral, as well as high frequency response. For the first test series reported here, the aim was high quantum efficiency, thus, lowly doped n-type substrates leading to long diffusion lengths of holes were selected. This leads to low frequency response and a quantum efficiency almost insensitive to reverse bias, due to the very long diffusion lengths of carriers in lowly doped material. Propagation loss for the multimode waveguides was less than 0.5 dB/cm for lambda greater than 700 nm. The dark current of the photodiodes was less than 100 pA and the breakdown voltage above 200 V. In a spectral range from 500 - 1000 nm, the devices showed very flat response with quantum efficiencies up to 82%. In the work now in progress, a p-i-n structure will be used, in order to optimize both bandwidth and quantum efficiency.