The purpose of this study was to evaluate if the maturity of biotech companies affect their stock return volatility. To do so, a new measure of maturity, from clinical trial data, was developed. Results show that maturity positively affects stock return volatility. To account for technological advancement, the maturity measure adds different weight to the number of drugs in the clinical trial phases. Moving a drug forward in the trial phases requires increasing amounts of R&D investments, combined with a high risk of failure.This is a possible explanation to the positive association between maturity and volatility.