The present invention is concerned with substituted imidazo[1,5-a][1,2,4]triazolo[1,5-d][1,4]benzodiazepine derivatives of the formula I wherein R1 is hydrogen, halogen, lower alkyl, lower alkyl substituted by halogen, lower alkoxy, lower alkoxy substituted by halogen, nitro, cycloalkyl, —O(CH2)mO(CH2)mOH or —C≡C—R′; R2 is hydrogen or methyl; R3 is lower alkyl, lower alkyl substituted by halogen, lower alkenyl, lower alkenyl substituted by halogen, lower alkynyl, —(CH2)n-cycloalkyl, —(CR′R″)m—CH3, phenyl that is unsubstituted or substituted by halogen, pyridinyl or thienyl each of which is unsubstituted or substituted by lower alkyl, —(CH2)n—NH-cycloalkyl, lower alkenyl-cycloalkyl, lower alkynyl-(CR′R″)mOH, or lower alkynyl-phenyl wherein the phenyl ring is unsubstituited or substituted by halogen, CF3, lower alkyl or lower alkoxy; R′ is hydrogen or lower alkyl; R″ is hydrogen, hydroxy or lower alkyl; n is 0, 1 or 2; m is 1, 2 or 3; and o is 1 or 2; and pharmaceutically acceptable acid addition salts thereof. This class of compounds have high affinity and selectivity for GABA A α5 receptor binding sites. Thus, the invention also relates to methods of enhancing cognition and treating cognitive disorders like Alzheimer's disease.