The article discusses the specifics of data exchange in the UHF band RFID systems using semi-passive transponders. In addition to the antenna and the RFID chip, there is also an additional source of energy (eg. battery) in the structure of such transponder. The battery may be used to implement additional functions such as the ability to measure physical quantities (eg. temperature, humidity). In this regard, particular attention was paid to the discussion of phases of communication between transponder and RWD associated with additional data (measurement results). An analysis of transmitted data frames has been presented. The preliminary results of the measurements have shown that the number of memory block transmitted from transponder has an impact on the effectiveness of RFID system.