This work reports that silicon/porous silicon mixed substrates can be successfully used for monolithic integration of RadioFrequency (RF) passive and active devices. To validate this concept, RF low pass filters for interference filtering between 0.9 and 2 GHz and electrostatic discharge protection diodes were integrated on 600 mixed substrates. At first, the electrical characterization revealed that both active and passive components integrated on the mixed substrate are fully functional. In addition, it was shown that filter performances are clearly improved if the passive devices are integrated on localized porous silicon instead of on lossy p+-type silicon.