This paper surveys 1/f noise in homogeneous semiconductor samples, distinguishing between mobility noise and number noise. It shows that mobility noise always exists with an α value in the order of 10⁻⁴. Damaging the crystal significantly increases α. Several theoretical models are discussed, but none explain all experimental results. α values for various semiconductors are given, which can be used in device noise calculations. The paper discusses four types of noise: thermal noise, shot noise, generation-recombination noise, and 1/f noise. 1/f noise has a power spectral density proportional to f⁻γ, where γ is typically 1. The origin of 1/f noise remains debated. The paper focuses on 1/f noise at room temperature (300 K) and discusses the factor α/N, which is crucial for understanding 1/f noise. α is a normalized measure of relative noise in different materials, and its value depends on crystal quality and scattering mechanisms. The paper also discusses the experimental distinction between Δn and Δμ noise. It shows that mobility noise is always present and is described by α values in the order of 10⁻⁴ in perfect material. Surface and bulk effects are discussed, with experimental data suggesting that surface effects may be more significant in some cases. The paper also presents models for mobility noise, including local interference noise and quantum 1/f noise, and discusses their applicability to semiconductors. Empirical values of α are presented, showing that α values for semiconductors range from 10⁻⁶ to 10⁻³. The paper concludes that mobility 1/f noise is always present in semiconductors with an α value of about 10⁻⁴. Damaging the crystal increases 1/f noise, while mobility remains largely unchanged. The paper emphasizes the importance of distinguishing between mobility and number noise in understanding 1/f noise in devices.This paper surveys 1/f noise in homogeneous semiconductor samples, distinguishing between mobility noise and number noise. It shows that mobility noise always exists with an α value in the order of 10⁻⁴. Damaging the crystal significantly increases α. Several theoretical models are discussed, but none explain all experimental results. α values for various semiconductors are given, which can be used in device noise calculations. The paper discusses four types of noise: thermal noise, shot noise, generation-recombination noise, and 1/f noise. 1/f noise has a power spectral density proportional to f⁻γ, where γ is typically 1. The origin of 1/f noise remains debated. The paper focuses on 1/f noise at room temperature (300 K) and discusses the factor α/N, which is crucial for understanding 1/f noise. α is a normalized measure of relative noise in different materials, and its value depends on crystal quality and scattering mechanisms. The paper also discusses the experimental distinction between Δn and Δμ noise. It shows that mobility noise is always present and is described by α values in the order of 10⁻⁴ in perfect material. Surface and bulk effects are discussed, with experimental data suggesting that surface effects may be more significant in some cases. The paper also presents models for mobility noise, including local interference noise and quantum 1/f noise, and discusses their applicability to semiconductors. Empirical values of α are presented, showing that α values for semiconductors range from 10⁻⁶ to 10⁻³. The paper concludes that mobility 1/f noise is always present in semiconductors with an α value of about 10⁻⁴. Damaging the crystal increases 1/f noise, while mobility remains largely unchanged. The paper emphasizes the importance of distinguishing between mobility and number noise in understanding 1/f noise in devices.