多晶硅，是由细小的单晶硅构成的材料。它不同于用于电子和太阳能电池的单晶硅，也不同于用于薄膜设备和太阳能电池的非晶硅。

在单晶硅中，晶体框架结构是均匀的，能够由外部均匀的外貌来辨识。在单晶硅（也称单晶）中，整个样品的晶格连续不间断，且没有晶界。大的单晶在自然界中是极其罕见的，并且也难以在实验室中制造（见重结晶）。相比之下，原子在无定形结构中的位置被限制为短程有序。

多晶和次晶相（见多晶体）由数量众多的小晶体或者微晶构成。多晶硅是一种由许多的较小硅晶构成的材料。多晶体晶胞可由一种可见的“片状金属效应”来识别纹理。半导体级（也包括太阳能级）多晶硅被转换为“单晶”硅——意味着在“多晶硅”中随机联接的晶体转变成了一个大的“单晶”。单晶硅被用于制造大多数硅基微电子设备。多晶硅能够达到99.9999%纯度。超纯多晶硅也应用在半导体工业里，比如2至3米长的多晶硅棒。在微电子业（半导体产业），多晶硅在宏观尺度和微观尺度（组分）皆有应用。单晶硅的生长工艺包括柴可拉斯基法、区熔和布里奇曼法。

Polycrystalline silicon, also called polysilicon or poly-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry.

Polysilicon is produced from metallurgical grade silicon by a chemical purification process, called Siemens process. This process involves distillation of volatile silicon compounds, and their decomposition into silicon at high temperatures. An emerging, alternative process of refinement uses a fluidized bed reactor. The photovoltaic industry also produces upgraded metallurgical-grade silicon (UMG-Si), using metallurgical instead of chemical purification processes. When produced for the electronics industry, polysilicon contains impurity levels of less than one part per billion (ppb), while polycrystalline solar grade silicon (SoG-Si) is generally less pure. A few companies from China, Germany, Japan, Korea and the United States, such as GCL-Poly, Wacker Chemie, OCI, and Hemlock Semiconductor, as well as the Norwegian headquartered REC, accounted for most of the worldwide production of about 230,000 tonnes in 2013.