A 94-year-old Australian man facing paedophile charges in Thailand has died while awaiting trial.

German-born Karl Joseph Kraus, from Western Australia, was suffering from prostate cancer and dementia when he died on Thursday, four years after his arrest on charges of sexually assaulting four Thai girls at his home near the northern city of Chiang Mai.

Karl Joseph Kraus in Thailand during his arrest. Credit:Am Sandford

Kraus had been giving English lessons to the girls, aged five to 15.

Chiang Mai-based legal sources told AAP that Kraus's lawyer had been preparing to appeal his detention on the basis of declining health and memory loss.