In order to assess if CA was converted into carnosol during extraction, we examined the purities of CA and carnosol in the extracts (Table 2). When extraction is performed at 40 °C or at boiling temperature (78 °C), the proportions of CA are higher than carnosol. The extracts obtained by MW at 125 °C contain more carnosol than CA: 3.36 ± 0.07% and 2.53 ± 0.17% respectively (Table 2). At 150 °C, purities in CA and carnosol are very similar: 2.17 ± 0.66% and 2.04 ± 0.02% for CA and carnosol respectively. It can be concluded that the decrease of CA in extracts does not result in a systematic increase of carnosol. Other minor degradation derivatives of carnosic acid are epirosmanol [35], 7-methyl-epirosmanol [36] and probably rosmanol 9-ethyl ether [37]. Other degradation products of carnosic acids such as rosmanol and rosmaridiphenol are also generated from carnosic acid during process. Moreover, it has to be underlined that carnosol naturally occurs in rosemary leaves [4], which could explain the concentration of carnosol found at lower extraction temperatures (Table 2). Globally, our results indicate that higher pressure and intensification through microwave and US probe favors a higher ratio of carnosol compared to carnosic.