We report on switching properties in the microwave region of yttrium hydride. A microstrip line of gold on a quartz substrate was used. A gap in the gold had an yttriurn hydride layer of 1.0 mum thickness with a cap layer of 5 nm palladium and 2 nm alummium oxide. The yttrium hydride was switched between a metallic and a semiconducting state with the exchange of hydrogen. The transmission (S-21) and reflection (S-11) coefficients were measured in the range 10 NHz-20 GHz. In the metallic state, the sample works like a microwave transmission line and in its semiconducting state, like a microwave resistor. The transmission coefficient was also measured at 5.0 GHz during hydrogenation and de-hydrogenation. (C) 2004 Elsevier B.V. All rights reserved.