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2. STOCK-BASED COMPENSATION - Fair values of the ESPP shares (Details 2) (Employee Stock Purchase Plan, USD $)
9 Months Ended
Feb. 28, 2015
Feb. 28, 2014
Volatility, Minimum 55.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum 86.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum
Volatility, Maximum 83.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum 100.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum
Expected dividend $ 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments $ 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments
Risk-free interest rates, Minimum 0.04%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum 0.04%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
Risk-free interest rates, Maximum 0.53%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum 0.33%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
Estimated forfeiture rate 0.00%AEHR_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsEstimatedForfeitureRate 0.00%AEHR_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsEstimatedForfeitureRate
Weighted average grant date fair value $ 1.47us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 1.34us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Minimum
   
Expected term (in years) 6 months 6 months
Maximum
   
Expected term (in years) 2 years 2 years