The direct detection of extrasolar planets is the only technique that leads to the most complete characterization of their physical properties. Here, we report on mid-IR observations of five directly imaged substellar companions (DF Tau B, FU Tau B, κ And b, GJ 758 B, and GJ 504 b) obtained with the Si-2 filter (8.7 µm) in the CanariCam instrument mounted on the 10-m Gran Telescopio de Canarias (GTC). We show the detection of FU Tau B, and we set upper limits of 11.5-12.0 mag in the 8.7 µm band for the other substellar targets. These data are useful to constrain their effective temperature and the presence of mid-IR flux excesses that may be due to surrounding disks.