Hydrogen trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized by secondary ion mass spectrometry (SIMS) and the desorption energy of hydrogen (Ed) trapped by the IPs was identified by thermal desorption analysis (TDA). Hydrogen trapped in metals often causes a degradation so-called hydrogen embrittlement (HE). However, it is very difficult even with SIMS to visualize the exact hydrogen trapped in metals, because hydrogen background (HBG) exists even in high vacuum chambers and also on sample surface, mostly in the form of H2O. To avoid the interference of the HBG, we performed a unique continuous pre-sputtering (pre-digging) by SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample. We succeeded in visualizing the exact signal of hydrogen trapped by IPs at the subsurface layer of the sample charged in high-pressure hydrogen gas. The TDA also clarified that the value of Ed was 200 kJ/mol or higher, which was extremely higher than the values of Ed for lattice interstice, dislocations, and vacancies. High hydrogen concentration was trapped at IPs in the subsurface layer in contact with the hydrogen gas. This trapping nature causes an extremely low effective hydrogen diffusivity of the 6061-T6, of the order of 10-14 m2/s even at 200oC. It may eventually give a high HE resistance for this alloy.