The front-end processing of the signals from the silicon strip detector in the BTeV experiment at the Fermi National Accelerator Laboratory (Fermilab) will be performed by custom-designed ICs. The readout chip has been developed in the frame of a collaboration with the University of Pavia, the Istituto Nazionale di Fisica Nucleare and the Electrical Engineering Department of the Particle Physics Division at Fermilab. The Fermilab Silicon Strip Readout (FSSR) chip is a mixed-signal circuit occupying an area of 7.27 x 4.46 mm2. The analog section of the FSSR core consists of 128 channels, each connected to a detector strip. The signals from the strips, after amplification and shaping, are compared to a preset threshold, generating a logic 1 at the output if a signal exceeding the threshold is detected. A symmetric baseline restorer is included to achieve baseline shift suppression but it can be bypassed by a programmable switch. An additional 3 bit information is provided by a flash-ADC. The charge sensitivity of the channel can be programmed either to 100 mV/fC or 150 mV/fC by acting on the preamplifier feedback capacitance and the peaking time of the signal at the shaper output can be selected among three values (60 ns, 85 ns, 125 ns). In this way the noise performances of the chip can be optimized according to the signal occupancy, preserving the required efficiency. The chip was designed and fabricated in the TSMC CMOS 0.25 um technology. Such a process, which features the intrinsic radiation hardness properties typical of deep submicron technologies, can be made even more radiation resistant by means of proper layout solutions, such as enclosed NMOS transistors and guard rings. The analog section of the chip was simulated and optimized from the standpoint of noise, comparator threshold dispersion and sensitivity to variations of process parameters. The first FSSR prototype was submitted in July 2003 and a second version of the chip, namely FSSR2, has been submitted at the end of 2004. During 2005 this second version has been thoroughly characterized through charge scan tests for equivalent noise charge (ENC) and threshold dispersion measurement. Results were found to be in agreement with the design specifications. In order to investigate whether the circuit is suitable to be operated in harsh radiation environment, some sample of the FSSR2 were exposed to gamma-rays from a cobalt 60 source. Irradiation did not seem to affect to any extent the properties of the circuit confirming the extremely high radiation tolerance featured by the FSSR2 chip.