This paper proposes an extendable front-end readout chip (EFRC) for electroencephalography (EEG) measurements. An EFRC is developed for EEG measurement with features including low power consumption, a high signal-to-noise ratio, and highly efficient chip area usage. A chopper-stabilized differential difference amplifier (CHDDA) is used in the first stage to amplify signals and then during another adjustable amplification stage and filter are used to process biomedical signals. A 10-bit successive approximation register analog-to-digital converter (SAR-ADC) then links to the back-end for digital signal processing. In the last stage, shift-register pairs are used to transmit data to the next chip and receive data from the previous chip. The shift register design allows the number of channels to be extended. A TSMC 0.18 um CMOS process is used to design the EFRC and it operates with a 1.8 V supply voltage. The results shows that the total power consumption for the EFRC chip is approximately 80.268 uW and the chip area is approximately 944 × 863 um2.